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Abstract: Transition metal dichalcogenides (TMD) have been one of the best alternatives as low friction coatings for tribological applications, particularly in dry and vacuum environments. However, besides their deficient behavior in humid containing atmospheres, their extensive application has also been restricted due to their low load-bearing capacity. In order to overcome these problems, recently the alloying with C has been tried with the expectation of simultaneously improving the coatings hardness and reaching sliding contacting phases more convenient for achieving low friction in humid environments. The practical application of this concept was extensively studied with the W–S–C system, with the C addition being achieved either by reactive or co-sputtering processes. The best tribological results were obtained by co-sputtering from a C target embedded with an increasing number of WS2 pellets. Excellent results were reached from the more than one order of magnitude increase in the coatings hardness up to friction coefficients which are close to those of the references of self-lubricating coatings: TMD for dry or vacuum atmospheres or C-based coatings for terrestrial sliding conditions. Following the good results achieved with W–S–C system, other TMDs systems have been envisaged to be studied. The main focus was placed on the Mo–Se–C system. In this paper, the general comparison between W–S–C and Mo–Se–C coatings is presented. The main effort is pointed on the tribological behavior of both systems when tested by pin-on-disk against steel counterpart balls under different testing conditions: applied normal loads, temperatures and relative humidity of the atmospheres. Both coatings were deposited by co-sputtering from a C target with a varying number of TMD pellets which could lead to C contents in the films in the range from 30 up to 70at.%. A Ti interlayer was interposed between the films and the substrates for improving the adhesion. Typically, W–S–C films are harder than Mo–Se–C films. From the tribological point of view, W–S–C films are more thermally stable than Mo–Se–C films although the friction coefficients of these last ones are lower when tested in humid containing atmospheres. [Copyright &y& Elsevier]

Abstract: Mo–Se–C films were deposited by sputtering from a carbon target with pellets of MoSe2. In addition to the standard evaluation of their chemical composition, structure, morphology, hardness and cohesion/adhesion, the core objective of this paper was to analyze the tribological behavior of these films, particularly in the high-load regime. The carbon content varied from 29 to 68 at.% which led to a progressive increase of the Se/Mo ratio and the hardness. The friction coefficient of Mo–Se–C coatings clearly decreased with load from ∼0.15 to ∼0.05. The excellent friction properties were attributed to the formation of a thin molybdenum diselenide film on the top of the wear track of the coating and on the counterpart surface, while the role of the carbon in the sliding process is only secondary by increasing the coating hardness and thus its wear resistance. [Copyright &y& Elsevier]

Recently, a new class of coatings based on oxynitrides has drawn much attention in the research field as well as in industrial applications, as shown by either the large numbers of recent publications on TM O N systems (TM—transition metal) such as Ti-O-N, Zr-O-N and Ta-O-N, or the development of Si O-N for opto-electronic devices. The properties of these coatings are related to the chemical composition and the structural arrangement. However, the knowledge about the structure of TM-O-N systems is very limited, especially how the structural arrangement of the non-metallic elements is in the lattices. To the best of our knowledge, only a few studies exist on the development of structural models for oxynitrides, based on XRD and/or XPS analysis, as e.g. Si-O-N and Ti-O-N, or on Mössbauer spectrometry for Fe-O-N. TEM was used scarcely for the characterization of TM-O-N coatings possibly due to the damage of the structure by the electron-irradiation as it is reported for Cr-O-N. This work is aimed at the crystallographic understanding of W-O-N sputtered films by using TEM and HR TEM techniques for complementing the information provided by XRD characterization. [ABSTRACT FROM PUBLISHER]

Abstract: Transition metal dichalcogenides have attracted considerable attention due to their self-lubricant properties. Their drawbacks, such us low load-bearing capacity or environmental sensitivity, have been partially overcome by alloying or doping with metals, carbon, or nitrides. Nevertheless, there is still a considerable potential for further improvement, since the majority of studies has been aimed at MoS2 and WS2 based coatings and the properties of diselenides remain almost unknown. Mo–Se–C coatings were prepared by non-reactive r.f. magnetron sputtering from carbon target with embedded MoSe2 pellets. The carbon content and Se/Mo ratio determined by electron probe microanalysis increased from 29 to 68 at.% and from 1.7 to 2.0, respectively, as a function of the decreasing number of pellets. The coating structure analyzed by X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy showed that Mo–Se–C was a mixture of amorphous carbon and Mo–Se phases, since no traces of molybdenum carbides were observed. Linear increase of the hardness from 0.7 (29 at.% C) to 4.1 GPa (68 at.% C) showed a significant improvement compared to values typical for pure MoSe2 coating. [Copyright &y& Elsevier]

Abstract: The thermal stability of different W–O coatings, W100, W90O10, W54O46, W30O70 and W25O75, were studied by in-situ X-ray diffraction at elevated temperatures up to 900 °C. The coatings were deposited by DC reactive magnetron sputtering from a pure tungsten target in an Ar+O2 atmosphere onto Fecralloy alloy. The evolution of the structure of the coatings was studied in both protective and oxidant atmospheres. Three groups of films were identified: (1) W25O75 which showed structural evolution following the W–O phase diagram; (2) amorphous O-deficient WO3 whose structure followed the W–O phase diagram either as WO3 or as its chemical composition depending on annealing in oxidant or protective atmospheres, respectively; and (3) low O-content crystalline films that oxidized from 500 °C. [Copyright &y& Elsevier]

Abstract: In this study, tungsten oxide coatings were deposited by dc magnetron sputtering onto steel, glass and silica substrates using either a conventional process (constant flow of oxygen) or pulsing of reactive gas (RGP). A square wave regulation signal with different pulsing period (T) and oxygen injection time (t on) was used in RGP. The partial pressure of argon was kept constant for all depositions. Three series of coatings were prepared: two with constant T and increasing t on and one with different T and constant t on/T ratio. The chemical composition, morphology and structure of these coatings were analyzed by electron probe microanalysis, scanning electron microscope (SEM) and X-ray diffraction, respectively. Preliminary studies have shown a linear relationship between t on/T and the oxygen content ratio (O/W) in the coatings. The structure of these coatings was a mixture of β-W (W3O) and quasi-crystalline WO3 phases in amounts depending of the oxygen content. SEM measurements have shown that a multilayer structure was obtained with increasing pulsing period. The hardness decreased with increasing oxygen content in the coatings. [Copyright &y& Elsevier]

Abstract: CrN coatings prepared by low arc deposition technology on hardened steel substrates were studied in this paper. Wear testing was done using a high temperature tribometer (pin-on-disc); the maximum testing temperature was 500 °C in order to prevent significant softening of substrate. Evaluation of friction coefficient with the number of cycles was measured at different temperatures and the wear rates of coatings and balls were determined. Three different materials were used as counter-parts: 100Cr6 bearing steel, Si3N4 and Al2O3 balls with a diameter of 6 mm. The coating microstructure was studied by X-ray diffraction (XRD) measured in situ up to 600 °C; the chemical composition was obtained by energy dispersive X-ray analysis (EDX). Mechanical properties of these coatings were studied by scratch and microhardness testing. Morphology of coating surface, ball scars, wear tracks and wear debris were examined by scanning electron microscopy (SEM). The experiments have shown strong dependency of tribological parameters on temperature. Wear of CrN coating sliding against the 100Cr6 ball was not measurable. Generally, the wear rate of coating increases with temperature when sliding with ceramic balls. The wear debris analysis has shown that the tribochemical wear is dominant at high temperature (Si3N4 balls), while the sliding process with the Al2O3 balls can be described as a three-body wear with the wear particles consisting mainly of chromium oxides conglomerated into relatively homogenous layer protecting coating from rapid wear. The average dimension of wear particles decreases with temperature, while the protecting layer thickness increases. [Copyright &y& Elsevier]

Abstract: Dry sliding wear experiments at specific temperatures ranging from 20 to 500°C were conducted on CrCN coatings deposited onto steel substrates. The coatings were worn against 100Cr6 bearing steel balls, Si3N4 and Al2O3 balls, using a pin-on-disc sliding configuration at a contact load of 5N. Friction coefficient and coating wear rates were measured, and wear tracks were analysed using SEM equipped with EDX. Coatings exhibited good wear performance and unexpected behaviour at elevated temperatures. [Copyright &y& Elsevier]

Abstract: PVD-coated instruments are often used at elevated temperatures. However, the friction and wear data of these coatings at temperatures exceeding room temperature are still lacking. In order to help remedy this lack, three coatings widely spread in industrial applications, TiN, TiCN and CrN, taken from standard production of customer''s coating centre were comparatively measured up to 500 °C. The coatings were deposited on hardened steel substrates either by unbalanced magnetron sputtering or arc evaporation deposition. The measurements were done using a high-temperature tribometer (pin-on-disc, CSM Instruments). The evolution of friction coefficient with sliding distance (number of cycles) was measured at different temperatures and the wear rate of the ball and coating were evaluated. 100Cr6 balls and the Si3N4 ceramic balls were used as counterparts. The wear tracks were examined optically and by SEM. The surface oxidation at elevated temperatures and chemical composition inside and outside the wear track was also measured by EDX analysis. [Copyright &y& Elsevier]

Abstract: Transition metal dichalcogenides are well known for their lubricating properties. MoS2 is the most popular member of this family and it is widely used as a solid lubricant in vacuum and inert gases. However, the lubricating properties of MoS2 are deteriorated in humid air. It is known that molybdenum diselenide (MoSe2) has the same crystal structure and also exhibits suitable lubricating properties, but their dependence on air humidity has not been studied yet in details. This paper is aimed to the comparison of tribological properties of MoS2 and MoSe2 coatings measured in air of different humidity and at elevated temperatures. Both coatings were prepared by non-reactive DC magnetron sputtering and tested with ball-on-disc high temperature tribometer. The results of measurements of friction coefficient and wear rate vs. tribometer revolutions and the resulting dependencies of friction coefficient and wear rate on ambient air relative humidity are presented. These results show that the friction coefficient of MoSe2 was not influenced by air humidity. Wear rate of MoSe2 in dry air was substantially higher than that of MoS2; in humid air, the MoS2 wear rate increased rapidly while wear rate of MoSe2 remained unchanged. The operating temperature of both coatings was limited to 350 °C. [Copyright &y& Elsevier]

Ideal biomaterials to fabricate orthopedic implants, especially for load-bearing joint replacements, should include only non-toxic elements with good biocompatibility, high corrosion resistance and surface bioactivity, together with a good combination of mechanical properties. Based on these criteria, a manufacturing approach based on sputtering techniques can be ideal to develop coatings free of toxic elements tailored for advanced applications on pure titanium or titanium alloys used in biomedical applications. In this work, the ternary Ti-Nb-Zr system was used to develop non-toxic β-rich Ti coatings with several complex microstructures by careful control of Nb and Zr concentration and deposition parameters, such as bias voltage. Depending on the alloy chemistry and processing, the coating included variable amounts of α- , α″- and β-phases of Ti with different morphologies and crystallographic texture. Mechanical properties of every coating is largely determined by the micro-structure present, which is directly related to bias voltage used during sputtering process. Thus, hardness values change as a function of the compressive residual stresses magnitude and Young's modulus decreased from 63 GPa, at 0 V, to 47 GPa, at −63 V, being this value close to human bone (~30 GPa). After that, Young's modulus progressively increases to 89 GPa, at −148 V. On the other hand, bioactivity of the coating is practically doubled when compared to Ti6Al4V alloy. [ABSTRACT FROM AUTHOR]

Hydrogenated diamond-like carbon coatings doped with tungsten were deposited by reactive magnetron sputtering from graphite and composite graphite/tungsten target in an Ar/methane atmosphere. Polished steel samples for laboratory testing and commercial valve tappets were used as substrates. The microstructure of the coating was studied by transmission electron microscopy (TEM), Raman spectroscopy, and electron energy loss spectroscopy, adhesion by scratchtest method and mechanical properties by depth sensing nanoindentation. Coatings were tribologically tested in lubricated contact in laboratory (pin-on-disc) and field (engine) conditions. The worn surfaces were analysed by Raman and time-of-flight secondary ion mass spectroscopies and observed by TEM. The coatings showed excellent wear resistance with negligible wear; the worn surface was covered by a very thin solid tribolayer formed from oil additives. [ABSTRACT FROM AUTHOR]

Abstract: Sliding properties of Mo–Se–C coatings with two different carbon content deposited by magnetron sputtering were investigated in different sliding environments (argon, nitrogen, dry and humid air). Both coatings had a structure that was identified as randomly oriented structures of MoSe2 embedded into amorphous carbon matrix. The worn surfaces, i.e. the wear tracks and the wear scars of the balls, were analyzed by optical microscopy, Raman spectroscopy and scanning electron microscopy. The material transferred to the ball steel surfaces was almost exclusively MoSe2, whereas the wear tracks on the coatings were more complex, with areas rich in MoSe2 and areas similar to that of as-deposited coatings. The friction was lowest in argon (0.012 at a load of 10N) and highest in humid air, but still remarkably low; as best 0.05 at 10N load; however, the exceptionally low wear rate was almost identical. Thus, we focused our detailed analysis on these two examples to understand the mechanisms responsible for the difference between the friction coefficients. SEM, EDX, XPS, Raman and TEM with EELS and EDX were applied to investigate the composition and structure of localized spots of interest on the tested surfaces. In both cases, we observed well-ordered MoSe2 tribofilms with negligible amount of oxides. Carbon was not present in the sliding interfaces, although large amount of carbon was found outside the contacts on both surfaces. Based on our investigations, we suggest the increase in friction of Mo–Se–C in humid air is primarily due to the increase in shear strength of the MoSe2 structure by the presence of water molecules in the sliding interface. [Copyright &y& Elsevier]